Income Support to Pension Credit

Where somebody reaches pension age and is no longer entitled to claim IS but PC instead; what happens or what should happen to their claim? Are there any provisions for it to be converted or at least contacted?

I am assisting a lady who was claiming IS which ceased but whose SRP is 90 odd quid and has no further income/capital so has been missing out for several months. She is also eligible for SDP so is a substantial amount of money.

I’ve little experience with pensioners myself so not come across this before but doesn’t seem right