#Python, 261 260 bytes

def c(s,t='bpcgdtfvgksz'):
 q,r,t='aeiouy',range(len(s)),t+t[::-1]
 c=[i for i in r if i>[j for j in r if s[j]in q][0]and s[i]not in q][0]
 C=([t[2*i+1]for i in range(12)if s[c]==t[i*2]]or s[c])[0]
 return s[:c+1]+(C+s[[i for i in r if i>c and s[i]in q][0]])*2

A Non regex, Not esoteric solution. Took about 20 minutes to make, and an hour more to golf.

It probably has more list comprehension than the entire python standard library, mostly because I don't know regex...

Try it online! (With testcases)

Python, 261 260 bytes

def c(s,t='bpcgdtfvgksz'):
 q,r,t='aeiouy',range(len(s)),t+t[::-1]
 c=[i for i in r if i>[j for j in r if s[j]in q][0]and s[i]not in q][0]
 C=([t[2*i+1]for i in range(12)if s[c]==t[i*2]]or s[c])[0]
 return s[:c+1]+(C+s[[i for i in r if i>c and s[i]in q][0]])*2

A Non regex, Not esoteric solution. Took about 20 minutes to make, and an hour more to golf.

It probably has more list comprehension than the entire python standard library, mostly because I don't know regex...

Try it online! (With testcases)

#Python, 261 bytes

def c(s):
 q,r,t='aeiouy',range(len(s)),'bpcgdtfvgksz'
 t=t+t[::-1]
 c=[i for i in r if i>[j for j in r if s[j]in q][0]and s[i]not in q][0]
 C=([t[2*i+1]for i in range(12)if s[c]==t[i*2]]or s[c])[0]
 return s[:c+1]+(C+s[[i for i in r if i>c and s[i]in q][0]])*2

A Non regex, Not esoteric solution. Took about 20 minutes to make, and an hour more to golf.

It probably has more list comprehension than the entire python standard library, mostly because I don't know regex...

Try it online! (With testcases)

#Python, 261 260 bytes

def c(s,t='bpcgdtfvgksz'):
 q,r,t='aeiouy',range(len(s)),t+t[::-1]
 c=[i for i in r if i>[j for j in r if s[j]in q][0]and s[i]not in q][0]
 C=([t[2*i+1]for i in range(12)if s[c]==t[i*2]]or s[c])[0]
 return s[:c+1]+(C+s[[i for i in r if i>c and s[i]in q][0]])*2

A Non regex, Not esoteric solution. Took about 20 minutes to make, and an hour more to golf.

It probably has more list comprehension than the entire python standard library, mostly because I don't know regex...

Try it online! (With testcases)

#Python, 261 bytes

def c(s):
 q,r,t='aeiouy',range(len(s)),'bpcgdtfvgksz'
 t=t+t[::-1]
 c=[i for i in r if i>[j for j in r if s[j]in q][0]and s[i]not in q][0]
 C=([t[2*i+1]for i in range(12)if s[c]==t[i*2]]or s[c])[0]
 return s[:c+1]+(C+s[[i for i in r if i>c and s[i]in q][0]])*2

A Non regex, Not esoteric solution. Took about 20 minutes to make, and an hour more to golf.

It probably has more list comprehension than the entire python standard library, mostly because I don't know regex...

Try it online! (With testcases)

#Python, 261 bytes

def c(s):
 q,r,t='aeiouy',range(len(s)),'bpcgdtfvgksz'
 t=t+t[::-1]
 c=[i for i in r if i>[j for j in r if s[j]in q][0]and s[i]not in q][0]
 C=([t[2*i+1]for i in range(12)if s[c]==t[i*2]]or s[c])[0]
 return s[:c+1]+(C+s[[i for i in r if i>c and s[i]in q][0]])*2

A Non regex, Not esoteric solution. Took about 20 minutes to make, and an hour more to golf.

It probably has more list comprehension than the entire python standard library, mostly because I don't know regex...

Try it online! (With testcases)