To apply for a visitor visa you need to be a genuine visitor. Comeing in with the intention to apply for an 820 would fail the "genuine" test and therefore would be denied.
Your partner needs to genuinely meet the requirements of a visa that is granted without a no further stay restriction. Once on shore she can then apply for an 820. Her bridging visa would only kick in once the original visa expires. If she does get a bridging isa then yes she will be able to stay until a decision is made on her 820.
*note you won't get to choose if the no further stay clause is added.
Your partner needs to genuinely meet the requirements of a visa that is granted without a no further stay restriction. Once on shore she can then apply for an 820. Her bridging visa would only kick in once the original visa expires. If she does get a bridging isa then yes she will be able to stay until a decision is made on her 820.
*note you won't get to choose if the no further stay clause is added.