14 week old can’t be left alone

My 14-week-old Lab puppy can’t be left alone. She’s crate trained and naps in the crate during the day and at night. During that time I can leave the room with no issue.

When she wakes up, we let her out as soon as we hear her move or whine — I don’t want her to think barking gets her out.

I’ve been practicing short separations: I say “back soon,” leave the room (she’s not in the crate), close the door, and set a timer. The longest I’ve managed is about 1 minute 15 seconds, and I can’t hit that consistently.

When I come back, I say “good girl” and give a treat. If she barks before I return, I go in and ignore her.

I need to be able to leave the house for errands, but I can’t even leave the room yet. What should I change or focus on next?

Any step-by-step advice from people who’ve worked through this would be really appreciated.