Is it permissible for my friend to lie to cover for me, after my repentance and seeking her forgiveness, when someone asks her about my previous lie to her?

All praise is due to Allah who bestowed upon you the grace of repentance. Your friend can use allusive language (ma'areedh) to avoid lying, based on the statement of 'Umar (may Allah be pleased with him): "Indeed, in allusive language there is a way out from lying."