@Imran67 I did a bit of sleuthing, and while on first glance the listing looks legit, there is definitely no mention of an off-site security deposit anywhere.
Then I ferreted out something that is highly suspicious. There are 15 reviews on this listing, and when I cross-referenced to see the reviews this host had left for her past guests, none of those guest profiles seem to exist. The only one that does, was the most recent one, from Keith, and there was no review left for him by this host. This is altogether strange.
When cross-referencing reviews, it would be highly unusual, unheard of, really, for virtually all of the reviews to lead to non-existent guest accounts.
I would pass on this listing if I were you, it could be some kind of scam, or at the very least, seriously question the host about this, as well as why she wants a paypal security deposit and why that isn't mentioned in the listing.