Tax Credits and New claims

I am wondering if anyone has any experience with this.
I am advising a client who is due to have her PIP appeal heard in a couple of months. She lives alone so will become entitled to a SDP if she is successful.
She doesn’t want to make a claim for UC as she does not feel this is enough and has been told from a friend she can claim disability tax credits which i am translating as working tax credit disability element.
I have tried to look this up and found a rule on the turn2us website which says if she is receiving or is entitled to SDP she can still make a new claim for WTC. However I believe the SDP condition for legacy benefits as gone now and UC is the only option now.
What are peoples thoughts ?

SDP doesn’t have an independent existence - its a premium which exists within an award of IS/ESA/JSA/PC or HB. For example if you are receiving irESA and you become entitled to PIP at the appropriate rates, then you would also be able to get your SDP within the ESA. But if you are not getting any benefits you can’t just claim SDP on its own.

Up until 27/01/21, if you were getting the SDP within a benefit award, this meant that you were not allowed to claim UC and would instead be able to make a new claim for legacy benefits. This would perhaps have enabled a new claim for tax credits - but this would only apply if the SDP were actually included in an award and would not cover a case where a person was living alone and getting PIP but did not receive a legacy benefit award for the SDP to be part of. It’s kind of moot anyway because this rule no longer applies so people getting the SDP are now able to claim UC again and therefore can’t claim legacy benefits.

What benefits does the client get now? If the answer is “none” then UC is really the only show in town and her hypothetical entitlement to tax credits or the SDP does nothing for her.