Missing Horsfield, Barnet, North London

[Daviesbell]

We have lost an 11 year old female Horsefield tortoise from our secure garden in North London (Barnet) on 31 September. Up to then, she was happy wandering the garden and easily found in favourite 'nesting' spots. She is approximately 20cm nose to tail and is missing three toes on her front right claw (it appears to be birth defect).
We have undertaken finger tip search in garden and spoken to neighbours with no sign of her. Whilst, there is no obvious sign that she has dug deep, she was last seen in a raised vegetable patch where the soil is soft enough to dig deep with no shell exposed. She could have escaped out of the vegetable patch which is something our younger male Horsefield does often when he is loose in the garden. However, there have been absolutely no sightings of her since 31 September- not basking, no weeds trampled/eaten etc, no new nests.
The only two options are that she has been taken by a predator (but we have no seagulls or ravens in our area or fox, although unlikely in daytime?) or human (our garden is secure and we were in all day). We have not found any shell or flesh fragments to indicate an avian or animal predator has taken her.
Can more experienced keepers advise if Horsefields can dig very deep or advise on experience with predators in daytime? Our 11 year old son is distraught and we are very concerned as the weather is getting cold and it is bound to rain as we proceed into autumn. If she is still in our garden and dug very deep, we are fearful she will not survive hibernation outdoors. Any advice appreciated, many thanks.