Being as your contract apparently did not include the proper condition checklist YOU WERE NOT LEGALLY ENTITLED TO A SECURITY DEPOSIT FROM THEM!  

So im definitely looking for any other options. 

Once you sign that agreement, you have a legal and binding document.Some fees that are placed in addition to a percentage are to help reduce the agent's fees - especially if the expected commission will not provide the agent with an adequate paycheck after the broker's cut and other investments that the agent had to make in order to help the buyer purchase a home have been removed from the commission.The challenge of the buyer is to make sure they have the funds to pay the agent.

Our current rent is $2600 I want to offer to pay $3000 for as long as she wants 1-15 years and then pay $600k My main question is whether that type of structure of offer makes sense legally or technically or practically. 

I will definitely be using this for reference.https://realestatebees.com/mortgage-social-media-content/

I would not do anything without further legal advice. 

From the law, I see that since I didn't give them a copy of the checklist, the security deposit is not "legal".

I will definitely be in touch as i proceed in this process.

Recommendations for legal counsel specialized in RE transactions?

I'll definitely be speaking with a CPA in Mass.