How many people can Luthien make fall asleep? 

She's never had the chance to test.

"I should be able to project your voice through the whole mountain, though I'm unsure if waking up some people will wake up everyone affected if the prisoners fall asleep too..."

"I should be able to arrange a test - Angband probably has more people, but Nargothrond still has a lot, and everyone here will understand the value of making the entire enemy fortress fall asleep."

"As long as orcs and whatever else are close enough to elves and men."

"They are. The biggest issues will be the Ainur, probably moreso the dragon, though that's one creature... Huan could be a bit of a test at least, and everything that participates in Arda is vulnerable to the Song."

"Mm," she agrees.

"We'd need to make sure you had time to get the song to work, though."

"And the things that are harder to fight will likely require more time."

She nods.

...So there's the option the timeline usually steers toward of getting captured and Luthien tricking Morgoth but Mygwainor is finding she doesn't want Luthien dancing for other people. Okay brain. 

"We might be able to confuse them about your location - I can probably weave that into the same effect that'll project your voice everywhere. Make it impossible to determine where in the mountain you are, and that lack of a true location lets your voice ring out from every possible path."

"That seems like it would help."

"We should make back up plans, but that seems a decent first option for now."

Nod.

Some time on those, then - there's a lot of moving parts here, but fortunately also a lot of time to plan before the snow melts. A lot of time for Luthien to test her songs against crowds and learn new, more war-focused songs from the Noldor. Experienced generals too - none of them a fraction as experienced as Mygwainor, and none of them aware of her history, but they're able to suggest a wider variety of creative options and things to consider than the group can come up with alone.

Time to sharpen the rest of their arsenal as well. All their skills will need to be at peak.

She spends a lot of time drilling both Luthien and Finrod, has them practice fighting her alongside Huan. Going all out she saves for private spars - her Song is stronger than most would think a mortal's should be - but just fighting she's fine doing in public, and quickly attracts watchers who often then volunteer to help practice, providing groups to fight. Mygwainor also takes to ambushing Luthien outside of their spars - that at least is more light hearted, since she 'demands' a kiss every time she wins. 

(She is a better fighter by far than anyone else in Nargothrond, even just limited to mortal weapons. It makes her an odd number of friends, since she isn't hesitant about offering help.)

Everyone should see her Mygwainor's best qualities.

Snicker.

"You can ambush me too, you know."

"Hmm, maybe..."

"See if you can't hold me down."

"I'm sure I could find a way."

"I'll keep an eye out for it."

"You'll never see me coming."

Smirk. "If anyone can sneak up on me..."

"Or distract you."