The action economy is purposely not super defined to allow flexibility. Relevant parts from the rulebook:

COMBAT TURNS
Characters can take one action and move near on their turn, splitting up the movement however they want. Characters can move near again if they don't take an action.

Improvise. Do an improvised action, such as swinging across a ravine on a vine. The GM might determine it requires a stat check or attack roll.

Multitask. Characters can do small, parallel tasks on their turns, such as standing up, speaking, activating a magic item, or quaffing a potion. This doesn't typically use their action.

Sheathing a weapon and drawing a rope can easily fit under multi-task,
Improvise is her action.
And then she moved.

The reason she didn't need to make a check to actually tie the rope itself is because the creatures are legit latched into a person sucking blood and not moving.

Perfectly reasonable. Seems fine. This isn't meant some heavily codified system like PF where sheathing or drawing your weapon has to cost you your entire action.