If you stay with EE, you should not need to unlock the phone.
An alternative to the main networks are MVNO's (Mobile Virtual Network Operators). They are companies who supply SIM's in their own name but don't have their own mobile network. Instead, they "piggy-back" off the likes of Three, Voda, EE and O2. Assuming your phone is locked to EE, you should also be able to use an MVNO who piggy-backs off EE without unlocking the phone.
In the bad old days, many phones were locked to a network and also had network branding on the phone itself in in the software. More & more retailers/ networks are selling unlocked and unbranded phones now, so it's worth checking.
I have actually heard of a network quoting a charge to unlock a phone that was not locked in the first place.
I guess the main reason your other half is with EE is because coverage is good in the areas she mostly uses her phone?
In this case, the cheapest deals will probably be an MVNO who piggy-backs off EE.
If you have Plusnet BB (who use EE), you can get some decent deals for SIM only contracts with them.
For example, 4GB of data, unlimited texts and minutes, 30 day rolling contract, £9.00. They also, like Three, allow you to roam to certain countries and still use your allowance.
They also have a Smart Cap system so you cannot overspend beyond an agreed limit.
The advantage of a 30 day contract is that if you see a better deal, or want to move to a different network, you are not tied for a whole year.
See here for all the UK MVNO's and the networks they piggy-back off.
https://en.wikipedia.org/wiki/List_of_United_Kingdom_mobile_virtual_network_operators
If she wants a new phone, then first of all, work out how much the old contract cost her. You say she pays £25/ month. I guess the contract is for two years?
That would be 24 x 25 = £600 for the term of the contract.
Taking Plusnet's SIM as an example, the cost for the SIMO over two years would be 24 x 9 = £216. Thus leaving £384 for a new handset.
Amazon have the J5 2017 for just over £180:
https://www.amazon.co.uk/Samsung-Ga...id=1519039630&sr=8-1&keywords=samsung+j5+2017
There are other J5 models that are cheaper, but I think they are older models.
Just a word of caution if you are buying a Samsung phone and intending to travel with it. Some phones may be what Samsung call "regionally locked". Phones sold here for this market are regionally locked to Europe.
This is not the same as a network lock. That regional lock can be disabled by using a SIM of the same regional origin (in this case a UK SIM) by either placing or receiving a call lasting at least 5 minutes within the UK before travelling. After doing this, it can be used abroad.
For example, you buy a phone in HK (example) and bring it back to the UK. It will not work on a UK SIM unless you have first placed/ received a 5 minute call using an HK SIM before leaving HK.
Samsung have been doing this since 2013 to try & cut down on grey imports.
So, to conclude: she could buy a brand new J5, put enough into a savings account in 2 years time to buy another one and pay for a SIMO for 24 months, all for less than the amount EE charged her.
EDITED FOR CLARITY AND ADDITIONAL INFORMATION.
