Respectfully @GoldenGran I think you need to find more things to occupy your time, maybe some new hobbies, making new friends. I am assuming you don't go out to work? (You never said but it sounds like you're home a lot.) Maybe some volunteer work? I don't know your circumstances as you've not said a lot about yourself, just complained a lot about your busy 'mum of 2' daughter!
I don't mean to sound rude, and I am sorry if it comes across that way, but sometimes when peoples lives slow down, and they're not so busy, it can feel like a lifetime waiting for something, and especially waiting for a text or message back from someone.
My mother used to be on my case if I didn't ring her 4-5 times a week and go and see her 3 times a week. (When I was working 3-4 days a week and had 2 small children! And she never worked!! Ever. She was a SAHM/homemaker all her life) She would make sarcastic remarks like 'I thought you were dead!' and 'been abroad have you?' (after 48 hours of no contact!!!) and occasionally 'you'll wish you'd been in touch more when I'm dead! You will feel so guilty!' (That has never happened, because I KNOW I gave her a lot of my time - and patience!!!)
But yeah, back off and stop demanding so much attention from her. She has left home and has her own family. What about your other child? You say you have 2 girls... Are bothering the other one as much? Are you as annoyed with her? Or does she act a good girl and message you immediately?! 
Seriously, my 2 (also girls aged 30-ish) had a phase where they would take a day to message me back, and even now it can take half a day! I am used to it as I know they're busy and I don't mind... Sometimes they message first, sometimes I message them first, and I see them 3-4 times a month (sometimes I and DH go to them - sometimes they come to us.) I work part time (18 hours a week, and have a very small social life,) and they have very busy professional careers (that involve some travelling,) and a busy social life. I don't expect anything from them. They are independent adults, who flew the nest over a decade ago, and I don't expect them to always always text me back within 3 seconds.
YABVVVU, and you need to chill a bit, and back off. The poor woman has enough on her plate with 2 little ones!