Hi Sachin,
I guess your wife is joining from India , right? I am from India too and I used Uk NARIC (now Enic)
https://www.enic.org.uk/ through the “Visa and Nationality services to gain “statement of comparability “of qualifications- I got a statement to say my qualifications were equivalent to uk degree standards) , additionally also opted for the “English proficiency “ evaluation through the same site(visa and nationality) . They evaluate against CEFR standards(my degree was evaluated to C1) . As entry clearance only required CEFR level A1(which is at a lower level), I did not have to sit IELTS.In the meanwhile, pls ask your spouse to obtain a certificate/letter ( signed on a headed paper with university seal)from the university to state that the medium of instruction was in english(this helped in my case and submitted to Enic). On the Enic portal,All you have to do is register and upload your documents ( degree certificates , medium of instruction letter,transcripts, Mark sheets) and they do the rest and issue the statements via post.There is also also a faster turnaround service for an additional price . The website is self-explanatory.I never had to take IELTS for entry clearance or FLR extensions, so definitely better option than the IELTS. IELTS is only valid for 2 years where as the above is not time-bound.
I have to also say the above is entirely my opinion from my experience and I’m not sure of what the current guidance is , so follow whatever guidance you have received on your application.
If you want to make an urgent application IELTS maybe a better option.
There are also some excellent moderators here and they might want to add some additional useful I go. Hope this helps
Wishing you the very best and hope you join your loved one soon.
Best wishes
Nah