The renewed agreement contained her esignature, I signed it and sent it back. 2 months later she says the agreement isn't valid, she never received it and gave me 30 days to vacate so she can move in. can she do this? I've lived here 4 years

So you kept copies right ?Always document everything concerning a lease agreement. If you haven't got a copy of that lease agreement 'that she signed before you', then you are screwed. She is looking for a way out and it doesn't include you living there.

Tick

On the other hand, I assume you have renewed the lease 3 times previously. If you can prove that, the court may believe you that you signed the new lease and returned it. So, if you want to risk an eviction you can fight it. But, do you really want to live where you aren't wanted.

The whole idea of contracts is that each party keeps a copy signed by all parties.
You are going to have a tough time if this goes to court.
On the other hand, if I were the judge, I would be very suspicious of her conveniently saying she never got it AND just happens to want to move in - if that were true, why did she send it to you, and why didn't she call you as soon as she changed her mind, saying don't sign it?
She might say 'After I didn't get it back is when I decided I wanted to live there,' but I'm still not buying the story.

A judge might or might not be willing to listen to this, and I would say you have a less than 50% chance of winning, based on the all-important need for a signed copy, and how weak all the 'stories' will be.

Did you e-mail it back to her? If so, she chose the mode of transmission. The argument would go that she bears the risk of losing it.

Where are you getting this from? What law, where says you have such time frames?

The question here is whether a court will decide that the OP has a valid lease or not. Without a signed copy of that lease, then it doesn't exist. The court may look at past history of renewals to decide when one exists.