It's good practice to validate people's feelings in general. It is not our place to say their feelings aren't valid... it's how they express them that can cause the need for boundaries.

Try keeping it REAL short.

Examples:
1. I see.
2. I understand
3. That Makes Sense
4. I hear you.

Then go on your way. Seems like it would very difficult for her to end the conversation first if your response is that short.