She will not be able to apply for residence in his country as part of an unmarried couple unless you can satisfy all these requirements
are in a current, long-term relationship (ie at least 2 years);
are living together with your partner;
share responsibility with your partner for any children;
share financial responsibilities with your partner, such as a joint mortgage or tenancy agreement, a joint bank account or joint savings, and utility bills in both your names;
and your partner have visited one another's home country and family; and
you have made plans about living together in the UK with your partner.
There are also financial. English language and suitability requirements to be met.
You cannot at the moment meet these requirements. You say you intend to marry, does that mean that she is your fiancée now? If she is then your fiancée she can apply for a 6 month visa to enter the UK if you can show that:
you and your partner are aged18 or over at the date of application;
your partner must not be related to you in a way that means you could not marry in UK law;
you and your partner must have met in person;
your relationship must be genuine and subsisting;
you must be seeking entry to the UK to allow your marriage or civil partnership to take place;
any previous relationship must have permanently broken down (this does not apply to certain polygamous relationships);
you and your partner must intend to live together permanently in the UK;
you must meet the financial requirements; and
you must meet the language requirement.
If you were to marry within that 6 month period she could then switch her application to that of a spouse wishing to reside.
A spouse applying has a list of requirements to be met similar to those for the fiancée application. Neither the fiancée application nor the marriage application have a 2 year requirement.
I am afraid that you are unlikely to be able to get her residing in this country as your unmarried partner. As you both wish to get married then an extra benefit of getting married would be that it would become much less difficult for her to apply to reside in this country.
I hope this answer helps. Please feel free to ask further questions. Also I would be grateful if you would please rate my service. This will not close your question and I will continue to answer.