I have several people at work like this who make me want to beat my head against the wall
My usual strategy is to head off the conversation onto a completely new tack that will hopefully catch her interest:
Me: I'll be a bit skint this month, my car MOT is due
Her: Oh, make sure you get it booked into a garage
Me: Yes... ooh, did you see they've opened a new coffee shop up the road? I saw it the other day and thought 'ooh I must tell Denise, she's someone who really appreciates a good cup of coffee'...
Sometimes it works, other times I have to look at my watch and squeak 'oh no, my samples will be overcooked / I've got to send that email / etc' and leg it.