Lol, Valk is horrible vs Zoners, the trick is to do Spike chaser after a combo, once he gets up and tries to cross the screen with wolf, he is just GETTING ASKED to eat a 6DD/2DD in the face since he can't block during wolf dash.
Like in every matchup, don't whiff a sword with Lambda and you are fine, don't throw out her drive senselessly when Valk is fullscreen away, you are playing Lambda not Nu.
You have to play it smart and trap Valk with zoning abilities, Spike chaser and that spinning ground blade are good tools vs Valk after a combo.
If you do get cornered by Valk, IB>Gravity Seed should do it, Valk's blockstrings are horrible and it's easy to Gravity Seed out of it, after that it's a free 2.5k-3k combo.
2C is a good anti air tool if you are scared off 6DD/2DD Valk during wolf air dash, just don't spam it because it has horrible recovery as well.
As you said watch out for his long ass 5C, if it counter hits you prepare to eat a high damaging combo. 5C(CH)>236C>.... hurts really bad for Lambda.
If you are in the corner, TECH HIS THROWS AT ALL COSTS, VALK's throws in the corner are deadly and even if he has no heat he will rack up the heat during the throw combo for his air distortion so say good bye to 5k or more off your health. So tech them, if you eat a throw in the corner by Valk you are screwed.
Also on a side note, if Valk's do that retarded "n00b loop" alias 2A>nachtjager>rinse and repeat, then just Gravity Seed out, IB into Gravity Seed if necessary.
Avoid going CQC with Valk, his normals are better imo then yours and so are his air to air stuff. His j.214B has a fuck ton of priority and beats out everything you have in the air except barrier block and you can't punish it either so be careful.It's basically like Hakumen's hotaru which is unpunishable aswell minus the invincibillity frames.
Full screen away if Valk's press button's during wakeup, 5D(CH)>236C>...
will hurt Valk alot, even more if you can do TK crescent saber combos.
Also on the ground be careful not to whiff swords, Valk has Nachtjager and Nachtrosen, and both cover up much space when he does them, with NachtJager counterhit he can't do any decent damage except if he has meter to rapid into 2C>6B>5B>5C>236C>combo so be careful, it can do around 6k damage...and to top it off you can't block his 236C during that combo because Valk's 6B puts you into crouching state, and 236C combos when you are in crouching hitstun.
But in all honesty, this matchup isn't all to good for Valk, if you have basic zoning skills you shouldn't have that much off a problem.