Well it sounds as if reality is intruding on the world of 'love' - though I have my doubts about either of you understanding what you are about if you have got so far along the road to matrimony before knowing much / enough about each other. It sounds more like mutual sexual attraction than love. If she were in love with you , she would be taking this a lot more seriously and would be horrified about upsetting you.
You two must either come to a definite agreement about money before the wedding or call the whole thing off.
It seems to me as though she has not yet grown up. You don't say how old she is. Has she ever had to manage money at all? has she lived on her own and had to budget for rent , food etc.? if not then it may be that she is very inexperienced in the ways of the world and is likely to be very stressed and petulant if she isn't indulged any more either by herself or her family or you.
Pushing your incompatibilities under the carpet will not make them go away. You have to have a long and very serious discussion with her about it. Money problems are one of the major causes of marriage breakdown so you must not get married until you have resolved this issue. Discuss with her the importance of saving for eg a home, your children, education, for a nest egg to tide you over a possible pregnancy, bout of illness , future responsibilities towards your parents etc. She needs to show you that she takes this all seriously.
It may be that she is truly saving a lot towards the wedding in which case she is showing her commitment and trustworthiness. If however she says she is but in reality she isn't then you have proof that she is very immature and irresponsible. Don't put yourself in the position of not being able to respect your partner in life. Explain to her that you think you would both be made very unhappy if you tied yourselves to another person who fundamentally has a different attitude to life, that you would make her very unhappy and you don't want to do that. Explain that you will both tell your parents that you have mutually agreed to part. You may have to shoulder many expenses for the non existent wedding but so be it.
Examine what you say you like about her ;
she seems ' reasonable' - no she doesn't at all if she can't control her spending. ( reasonable sounds a very lukewarm comment to make about someone you purport to love to me.)
' not stuck up . show offy' - heavens buying shoes/ bags costing hundreds is not show offy!
If you are feeling anxious about all this now you will be a hundred times more anxious after the wedding if you have not solved the problem. However difficult, embarrassing it seems to break off the relationship now, it will be a hundred times more so after you have wed, have children . You really don't have the right to marry someone in such an irresponsible way because the failure of the marriage will impact on you, your wife, your children etc. Either one of you may eventually have to leave the relationship or worse one or both of you will feel forced to stay, unhappy and in despair, unable to have a meaningful relationship ever in your life.