So the thing comes down to that between Gunjan and Maayank, the marriage was PURELY Maayank's fault. If he signed the contract BEFORE the rounds then he was official married to Charu, so whether or not Gunjan took saat phere with him meant nothing. Legally he was Chaaru husband before Gunjan sent Chaaru in her place.
And if he signed it AFTER the 7 rounds then still his fault because he didn't have to sign it legally if he didn't want to marry Chaaru. He also had the excuse of her being a liar too so he could have refused.
And we know he didn't sign anything while Chaaru was hidden underneath the veil because we saw it with our own eyes he didn't sign anything.
So honestly it wasnt Gunjans fault at all. Yea she shouldn't have made Chaaru go in place of her but she
is totally not legally responsible for Maayank and Chaaru wedding.