Try this formula

=SUMPRODUCT(($A$2:$A$15=D2)/COUNTIF($B$2:$B$15,$B$2:$B$15&""))

Row\Col
A
B
C
D
E
2
 Joanna ECO60610 Joanna
1
3
 Joanna ECO60610 Ilona
3
4
 Joanna ECO60610 Sylwia
1
5
 Ilona ECO56003 Marta
1
6
 Sylwia ECO59237
7
 Sylwia ECO59237
8
 Sylwia ECO59237
9
 Sylwia ECO59237
10
 Sylwia ECO59237
11
 Sylwia ECO59237
12
 Marta ECO59824
13
 Marta ECO59824
14
 Ilona ECO60593
15
 Ilona ECO59298