Canasta Players

I play Canasta with a group that has one player who drives me crazy. She's what I call a "selfish" player. Example: We're partners and the meld is 120. The pile is getting deep when I finally manage to meld, leaving my hand with 5 cards. My partner picks up the pile on her next turn, then holds all the cards until she can go out, leaving me out of the game entirely. What is the point in this kind of play?