Unable to sign acknowledgement due to medication

So over 16 years I split up reasonably amicably and we managed to sort out splitting up finances and child maintenance without going legal. We both agreed we should get divorced but for one reason or another never got a round to it.
Few years ago met someone and would like to get married at some point and asked the ex if ok to start diy divorce proceeding and said yes no problem. I filled in the forms online and paid the fee and waited, got a response back sometime later to say she had not aknowledged the application. Contatced my son who told me that unfortunately she had an medical episode and was on medication which could cause psychosis and had been advised not to sign any legal papers.
Fours months later, I ask him if she can sign them now and he says she is still the medication and cannot sign them. The only next step I can see online if a respondant does not reply is to pay a baliff to present them to her but this isn't worth doing if she has a valide reason not able to sign, is there any other way I can proceed or do I have to wait for to eventually come of these meds?