Berkut's Lance Summer Robin?

If she's going to have a Berkut's Lance+ build, her A Skill probably has to be DC just to make her a 'Balanced' unit. I think Fury and a Spd Refine will just do. Also she's a unit in that's limited and not in the summoning pool, is there really a point of giving the lance to her if she has a Res Superbane.

Yes she can do it but she won't perform as well as other lancers who can do the same role but better.
I recommend to stay away from berkut's lance for now and build her offensively.

When under attack she'll have 32 Res which is pretty decent. If it's for use with DC as a mage tank and a speed refine she can do fairly well I'd say. If you're set on Berkut's Lance, another (cheaper) option is to aim at being an anti-dragon unit with a Res refine and Fury (or CD/Warding Stance) giving 39 Res when under attack and her speed will mean she doesn't fear doubling though may struggle to double F!Corrin, F!Kana and Summer Y!Tiki.

I would say with +Spd, an offensive build would probably be better to capitalise on her boon, but she's you unit, you don't have to listen to words on the screen.