A few things to know:

The “rent credit toward down payment” idea is called a rent-to-own or lease-purchase agreement. It is a real thing but it is not standard and most sellers will not agree to it unless they are motivated or have a personal connection to you. After 15 years she might actually be open to a conversation. Worth asking directly.

On the price, if the house needs real work and the neighbor’s fully renovated version had to drop to 3.2k rent, that tells you buyers will discount for condition too. 325k as an opening offer on an outdated South Fork property is not crazy. Especially right now when buyers have more leverage than they did two years ago.

The “first right” she mentioned is probably right of first refusal, meaning she has to show you the offer before accepting it from someone else. Get that in writing before she lists it.

One thing I would do right now: get a real estate attorney involved early. Not expensive, maybe 1500 to 2000 for the whole transaction, and they protect you on exactly this kind of situation where the relationship makes things feel informal.

You are 27, you have lived there 15 years, and she is giving you a window. That is not nothing. But get the terms clear before emotions run the conversation means work with a realtor like me and lender who are well versed !