If there are disproportionate deposits and withdrawals in the bank statements, they should be explained in the sponsor's letter. not really a good idea, unless you've got good reasons and evidence to show where the money came from, the embassy is not stupid, they know people will borrow money, put it in their bank for a while then pay it back.but
if you had little in your bank, then money appears, this could attract their attention and possibly a refusal, because they don't believe you have the finances to support her and will refuse you 'on the balance of probabilities' she will need recourse to public funds.
get it right first time, because refusal, appealing, re-appyling will cost you time,money and heart ache
probably better to get wed in the phils, as you will not need all the evidence of your proposed wedding in the uk,
if you wed, its cheaper in the phils, you've already made a commitment getting wed, and you have lots of evidence of a genuine relationship already. just a place for her to live (if you can live at your dads for a while) thne its just your finances - a job and some savings .