Pending deed of sale and car transfer

Hi guys, i am seeking for your kind assistance or legal advice regarding on my car which i bought from my previous officemate. The car is still on financing and will be settled by this quarter. What i have is witnesses, acknowledgement receipt of my cash dp to her. I was'nt able to secure a deed of sale since the car is a collateral and is not on her name yet. Now that the car is almost paid, using my own checks, the conflict arises. The previous owner does'nt want to cooperate on my request to give me a signed SPA and deed of sale of my car, not stating her reasons or intentions for resisting. Is there a way i can sue her or to force her to sign legally? What is the chances of this case to be reverse if she intends to reclaim the car? I Appreciate your opinions and advices, thank you in advance.

SPA for what?
once the financing was fully paid, the car will be named after her right?
then you can ask her to provide the deed of absolute sale later..
for the car will only be hers, upon full payment, and legally she can not sell something she don't own.
make clear arrangements, and have it written, specially if money is involved.
though you do not have the DOAS, as long you have other docs to prove you gave her money, etc,,
then its fine.. you can have it later.