I'm Lucy, and I'd be happy to answer your questions today.
Yes, you can demand a new check from the tenant. She has an obligation to pay the rent, and your mistake in forgetting to cash the check does not mean she gets a free place to live for that month. It would be different if you found the check after several years, because then there would be a statute of limitations issue, but there is no state where the statute of limitations is less than a year.
If the tenant refuses to issue a new check, and you can't (or don't want to), make arrangements for her to pay it off in installments, then you can serve her with a notice to pay or quit and proceed with eviction, just like if she hadn't paid you at all.
One note: if the check doesn't SAY it expires in 90 days on the face, it actually is still valid and can be cashed. But it could still help to talk to the tenant and make sure the funds are available before doing that.
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