Very timid cat- when can I let it outside ?

[Thirtyrock39]

I'm looking after my parents cat while they are in between house moves for a month or so , she is a very nervous cat will let us stroke her but not pick her up or sit in our laps (same with my parents)
With my parents she's outside the majority of the time come rain or shine
I was planning on keeping her inside for two weeeks but she is showing signs of frustration inside- pooed on the mat twice now (will also use litter tray) and miaowing a lot - my worry is she will bolt if I let her out and she's not tame enough for me to carry her round the garden etc ...won't always come when called for food etc etc
Any advice on how or when to introduce the great outdoors ?
She does have free run of our house but spends a lot of time hiding under beds at the moment so is still not totally relaxed (been here for nearly a week)

A week is not long enough to get used to a new place anyway, especially for a timid cat with new humans. She might well escape or try to find her way back to her usual home if you let her out. Best not to, and be careful with windows and doors to avoid accidental escapes.

The usual recommendation for staying in before going out in a new home is 4-8 weeks depending on the cat's personality.

If you only have her for a few weeks I wouldn’t let her out at all.

My newish rescue cat is scared of everything, I've had her since feb but still can't let her out, personally I'd keep the cat in, it won't do her any harm.

Sorry to say it, but poor cat ownership of your parents. Cats don't like change and it's not like you're adopting her.
If she likes being outdoors, why not get a lead and allow her to explore your garden?