1. Works fine, as long as she's a trustee. The trust is the applicant, not you.
2. Yes, you need them for the serial number and manufacturer info.
3. Barrel length. OAL is usually barrel plus ~19" for most setups.
4. Extended stock to furthest muzzle point, which would include a permanently attached muzzle device.
The actual wording on measuring OAL:
The overall length of a firearm is the distance between the muzzle of the barrel and the rearmost portion of the weapon measured on a line parallel to the axis of the bore.
And the proper methods of permanently attaching the muzzle device:
Permanent methods of attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver soldering, or blind pinning with the pin head welded over.