You will need to raise it with your solicitors. But remember the solicitor is now defending the estate of your mother, they are not exactly defending the beneficiary (though they kind of are if the beneficiary is also the executor). Without know all of the facts in detail no one can tell you there is a conflict, but it simply being the same solicitor is not automatically a problem.
If you have no money, you will struggle to pay your lawyer's initial fees (and you may therefore struggle to find representation). I am not a practicing UK solicitor but it is possible that that you will be required to give an undertaking as to costs as well.
No one here can tell you what you should do, all I can say is that unless the estate is worth a lot and your evidence as to capacity/undue influence is strong it is very likely you will lose more than you will gain.
Do you really want this dragging on for the rest of your life? Really?
Fight by all means, but just go in with your eyes open.
She is dead, gone, the relationship cannot be repaired, all you can do is either move on, or stay stuck in the same horrible circle.
Is it worth it?