If you still love BFing AND she is willing to take a bottle than I would not wean her yet. As best as possible start pumping some extra milk and freezing it for you mom. Even if she takes formula, I would still try to pump a little BM for her to have over night. Then, TAKE YOUR PUMP WITH YOU! You will be in terrible pain with out it. (Unless hubby wants to "relieve the presure" in them. hehe) I would most likely pump and dump while I was there, but that would have to be your call.
I was never good at pumping but I had to for 3 days after a medical proceedure that involved being injected with radio active dye. This happened right at my son's 1st b-day. For three days he could only have bottles, and I had to pump about 6 times a day. Finally on the 3rd pump of the 4th day my milk wasn't green anymore, so the next feeding he got me back. From that point on I nursed him with out any problems until I stopped him at 18 months.
If you still love it, than don't convince yourself that this HAS to be the end. Yes, she will probably cry to get some in the middle of the night, but your mom KNOWS she still wakes and is willing to care for her anyway. She and your mom will be fine. Your talking about 3 nights/4 days of not so perfect rest. Your mom loves you, and her, and will likely be just fine with it all.
Enjoy your trip~ J.
BTW- breast fed babies ARE hungery in the middle of the night. That's WHY so many of us BF Moms are exhusted until we stop doing it. BM is not as filling as formula. Formula fed babies sleep through the night from close to the start because that stuff hits their belly like Thanksgiving Dinner. So, if she cries, there IS a reason. SHE IS HUNGRY!! And it's not just about "wanting comfort" or "needing attention." If you woke up at 2am with hunger pains so bad they were keeping you awake, you'd likely go drink a glass of milk and go back to bed. She is NO different.