four months is not going to be a problem time wise. you can still file to annul the probate. whether you have the evidence is another matter. don't know if any attorney would wait for payment. I would not. how do I know that you are going to get anything in the end? and, you may well have expense in trying to prove it. may need handwriting expert. may need doctor if you feel he was not competent. so, yes you can try and fight but I doubt many attorneys will wait till the end for payment, but obviously I cannot speak for any one else.i would not.
I agree with what Mr. Maas said. In addition you may be entitled to inherit if you are a forced heir. If you are under 23 at the time of your father's death or if you are disabled in some way you may qualified to inherit as a forced heir. You should at least consult an attorney to discuss the matter.
Every situation is different and you should consult your own attorney to go over all the particular facts in your case. The answer given is only intended to provide general guidance regarding rights and responsibilities.
From your question, it appears your father's succession has not been opened, since you mentioned only being shown a will. My guess is that she is showing you the purported will to remain in possession of the residence and property and is likely not intending to open the succession. In that case, you will need to go to court to contest the will. You may be able to find an attorney to give you a free consultation, but it is unlikely that you will get an attorney to proceed without payment. That is something most often done in personal injury cases in which there is a high probability of a substantial settlement or judgment.