Not unreasonable at all OP. Interestingly, this is often a common theme over on MN, uninvited guests, who may never leave!!! One such thread, family lived in desirable part of the country, had visitors who invited themselves, for what seemed like quite a while, no gifts, no contribution to the household budget, dumping their washing by the machine. The advice was ask them to go and do a supermarket shop, which they eventually did, but left a receipt on the kitchen table for the hosts, which the hosts getting into their stride binned! Eventually after being spurred on by other posters, the guests were issued with this ultimatum "we'll make you a breakfast before you depart on Saturday" the freeloaders had no such intention of going, but that's how they were finally ousted.
Other than immediate family, who come and go on a regular basis, usually for the weekend, we sometimes have one or two close friends and extended family stay for a few days, always invited, these are never open ended invites, they never come empty handed and offer to buy us a meal out during their stay.
Everyone else has said it, you must be in control and put some rules in place and yes a bunch of flowers is a very paltry offering for such a stay, she should be prepared to chip in with all the extras such as food, I'd pose that diplomatically along with pinning her down to maybe a day or two and a definite date of departure to suit you, or if you don't fancy the visits say so with "I'm just not up to hosting anymore/at the moment" That should suffice, no more explanation required.
Good luck!