Who should take the next step?

10 days ago I had a date. Compared to all other dates I had in the past, was going super smooth, I can say that this time a real connection was made. We walked until the entry of her apartment and we kissed there a lot. She has a son and her sister was taking care about him during our date in her flat.

After I came home she said by text "thank you for the nice &very pleasant evening"
The day after we made plans for the subsequent day, but she cancelled that one.

Then I was traveling 3 days for work and she told me to contact me when I was available. I did (Thursday), but then she said that she couldn't make it that evening (maybe I asked it too short beforehand).

She gave several times the message that she wants to meet again.

Why is this situation bothering me now?
Let me make this clear: I'm not putting her on a pedestal, but I know that sometimes in the past I was too slow to initiate follow-up contact.
I read somewhere an article "Attraction has an expiration date", which said something like: you have to move fast in order not to lose her.
Should I contact her again (I don't want to be needy or pushing) or she me?
I would say that she now has to confirm her interest by being the one who contacts me.

Maybe I shouldn't be bothered with this question if I didn't now have a (exceptional) period of frequent work-related travel, thus limited availability from my side. I just don't want that this external factor might kill the attraction...

Ask her out again and if she can't do it at the time/day you suggest, ask her if she has any other dates that would be more convenient for her (she does have a child after all that she needs to get a sitter for). If she makes an excuse not to reschedule with you then don't contact her again. She's not interested or, even if she is, she has no time to nurture a relationship with you.

Give her one more chance and if she doesn't respond positively to your invitation then consider her having lost out on a good thing with you and just delete her from your contacts.

So, I called her this evening and we spoke on the phone for 10 minutes. The phone conversation happened in the same positive atmosphere as the date (with laughter). She thanked me three times for calling her. I think she appreciated it that I asked about her son.
However, she gave softly the message that probably the first day isn't possible (sorry, can't go into detail here). I didn't push/ask for a next meeting since I will be away for three days this week. So, I think/hope that we can meet the upcoming weekend.

So, she made yet another excuse to see you and didn't reschedule. Hmmmmm.

It's really okay to contact her again.

She might not have been able to get a sitter for other times asked ( her own sister sitting included ) ~ give another go but ask her to pick the day & time that works best for her instead.

So, last time I called her I did like breathe123 suggested and ask her to let me know what time would suit her. This wasn't a question out of the blue, because at that time she was telling me what she did previous weekend and that she wanted to show me pictures about it. She agreed to let me know the next day when it would suit her. This didn't happen.

There is a contradiction here:
On one hand she's very positive in her talks and also about seeing each other (she started about it last time), but until now this didn't became concrete.
But in case she doesn't like me she would/should make this clear.

Remember, what I said in my original message "Attraction has an expiration date"...

Stop calling her, or you will start to look like a little b*tch and she won't respect you. For whatever reason, she isn't interested. Make your judgements based on a person's behaviors rather than their words. People will lie to avoid hurting you or in order to avoid taking responsibility for their feelings..

Well, she contacted me again and invited me to a concert upcoming Saturday. I'm a huge fan of this band, but I already got other plans for Saturday evening (also a one time event).
Dilemma....

Don't be so quick to jump at her invitation. Tell her you can't make it as you have other plans (as you do). Don't reschedule anything with her but do call her sometime next week to see how the concert went and to ask her out on the weekend to go to something that won't take up too much time so that she has time to get a sitter and won't have to pay too much for same as she will only be away for a couple of hours.

If she turns you down then stop wasting your time on her for goodness sakes. There are lots of women out there that are single and motherless that will have the time and the inclination to be in your company. If she turns you down again then she is NOT one of them.