"Dominator Mech" from Supergirl and the Legion of Super-Heroes #26 (DC, 2007) by Mark Waid, Barry Kitson and Mick Gray
Volume 5 of the Legion of Super-Heroes turns into Supergirl and the LSH with #16, reverting only to its original name upon her departure as of #38. I missed most of this first time around (because I was out of comics entirely), but am now assembling this run which looks to be a lot of fun. Mark Waid's Supergirl AND Legion? It's worth a shot.