She should not be spending lots time in the UK than her home country in any 12 month rolling period. This would be considered residing and not visiting. If an IO at the airport sees she is staying here longer than her home country, her visa could be cancelled and she could be refused entry, which will make any future visitor visas difficult to get.
Also important to note that what she stated in her visa application as duration of stay is important. If she stated a visit of 1 month and then stays for 6, is not usually a good idea.
https://www.gov.uk/guidance/immigration ... itor-rules
Genuine intention to visit
V 4.2 The applicant must satisfy the decision maker that they are a genuine visitor. This means that the applicant:
(a) will leave the UK at the end of their visit; and
(b) will not live in the UK for extended periods through frequent or successive visits, or make the UK their main home; and
(c) is genuinely seeking entry for a purpose that is permitted by the visitor routes (these are listed in Appendices 3, 4 and 5); and
(d) will not undertake any prohibited activities set out in V 4.5 – V 4.10; and
(e) must have sufficient funds to cover all reasonable costs in relation to their visit without working or accessing public funds. This includes the cost of the return or onward journey, any costs relating to dependants, and the cost of planned activities such as private medical treatment.
