demi that is really shit and I think your mum really could have made a bit more of an effort, it is not everyday you turn 30!
If it was me, I would not ask her to mind then kids again, she has made it clear she doesn't want to, at least this time.
I think I would plan an evening of treats with my dh if I were you. I would be thinking along of the lines of getting the kids to bed as early as possible.
Then pretend that your bedroom is a hotel room for the night! Nice bath (together! Or at least with him soaping your back etc) with a bottle of bubbles, indulgent bath products and only candle light.
Then into bed with the best takeaway you know, more bubbles and lots of your favourite treats (birthday cake / chocolate - whatever floats your boat)
Clean bedding, flowers (even a supermarket bunch) romantic lighting, a pile of magazines, soft music or a good movie on tv / laptop etc. And just really take the time to chat and be together! Like a mini-break without leaving your own home!
coffee in bed the next morning!
I am basing this sort of on personal experience - we had no money for my 40th. Dh booked really cheap flights to Paris and a cheap, small hotel, it was winter and freezing cold sleety weather. We had walked about all day and were cold and tire, we came back to the hotel to get changed and dh wanted to bring me out for a meal, but I was worried about money and was feeling down about turning 40 (from a ttc point of view). He filled the bath for me and as I was lying there, enjoying just being there, I decided that I REALLY didn't want to go out at all.
Dh went out and got us a pizza from the Italian across the street (turned out to be THE best pizza we ever had! We went back a few years later and it was just as good) and a bottle of champagne which we ate and drank in bed (from the toothbrush glasses) and it was absolutely perfect. I still consider it one of my favourite birthdays ever!
Since then we have recreated it at home once or twice for either his birthday or mine and it has been great. It is nice to have an evening free of all the usual crap and to spend it laughing and cuddling etc.
Wishing you a very happy 30th whatever you decide to do!