I suspect that it's not going to be anywhere near as simple as that. I'd consult an attorney.
Among the issues that might enter into the discussion:
- I'm not sure what is required for eviction, but my guess is that 3 days won't be even close.
- The fact that they've allowed her to live their without paying rent or a lease for a long time is going to make it look like a gift. If she claims that it was offered to her as a gift in perpetuity, there's going to be a big court battle. Since you don't mention any written agreement, her word is as good as the property owner's (better, in fact, since it was the property owner's HUSBAND who made the agreement and he's not around). Admittedly, a gift of real estate is not binding unless it's in writing, but that doesn't mean she can't tie it up in the courts for a long time.
- While the kids are in college and are technically adults, in some areas, there's a tendency to treat college students as children - at least as far as support is concerned. The court may be sympathetic to the argument that they were offered the residence while the kids were dependent (thus, the 'until they graduate' statement), but that since they're still full time students, that they should still get the use of the residence.
- Real estate law, in general, has rules of its own and common sense doesn't always apply.
Granted, none of the above are particularly strong arguments, but an attorney would be able to deal with it properly rather than floundering around in the courts for ages (do you know how long it really takes to evict someone in CA? Although the notice period is small, the people I know who are landlords say it's typically 6 months or a year - or more).
Keep in mind that she's getting free rent. She has a huge incentive in making the current situation last as long as possible. You, OTOH, want it to end NOW. Any delay works to her advantage.