I actually had less problem with Serana as opposed to Marcurio... I'm shooting enemies with a bow and suddenly they go flying after I've shot my arrow, causing my shot to miss... Though I did learn to not have animals with me when I have Serana around... While she never hit me, Meeko wasn't so lucky ._.
Hate it when that happens! Just yesterday I restarted the Dawnguard questline, and at one point, after fighting some foes, Serana started to attack ME! I didn't even do anything to make her do such drastic things ;__; Normally she puts up with my shit, even if I accidentally hit her D: