If the worst comes to the worst, don't forget: I'm pretty sure that nobody likes things like weeds or stones. XD
Can't remember if she likes them in this game, but in (M)FoMT Popuri actually likes weeds. Don't think they up her friendship level much, but she smiles and thanks you for giving them to her...
Also Mark and Chelsea will accept anything with a smile, including weeds, stones and rubbish.
But your point is valid; most people hate recieving weeds and other refuse.
On the other hand, if you don't want to lower her friendship level, and you don't mind waiting, you could always wait until you're married to veiw the rival heart event. Then it doesn't matter how high their friendship levels are with you.