You never give immunity unless you know what she has to tell and part of the deal is that she tells what she knows under oath. If she waffles, no deal.
What’s the value of Congressional/Senate immunity? It’s not like John Dean et al. didn’t get prosecuted anyway.
Grant “immunity” depose her and then jail her and every one in the executive. Basically, lie and make up “The Law” as you go... I will even offerthe subcommittee doing the investigation a few pens and phones.