Send like a beginning of a genuine relationship. You met a girl a couple of times over a (lady's) drink, after the 3rd date you paid a bar fine and she came to your hotel (you didn't mention it it was over night or just short time - and there's a big difference between the 2), then you transitioned to long distance relationship and now you consider taking care of your sick future mother in law. That's nice. You should stay in this relationship as it seems she really like you so much that she disclosed to you her mother's medical condition and now it is up to you to show her how serious you are about her. You should offer her to move her mum to a better private hospital, maybe the big one in Bangkok so she can see how much you love her.
Another option is that you send her the 8k and tell her that's an advance payment for your future dates...