Tomoyo: A Friend With Her Own View
Tomoyo has interests of her own. Her position beside Sakura can produce observations that participation misses.
Spoilers throughout. This page assumes you have finished the series.
Tomoyo's support for Sakura is more interesting when it includes a preference of her own. Caring about someone need not make every shared activity an obligation to stand in the same place or perform the same task.
Choosing a position beside the action
The official character introduction identifies making Sakura's card-hunting clothes and filming her activities as Tomoyo's pursuits. Those are forms of involvement with their own work attached: producing something and recording something are not the same as merely being present.
In the official Clow Card archive, Tomoyo chooses filming over partnering Sakura in episode 34.
My reading of this small arrangement is that Tomoyo can choose how to participate without making Sakura's participation impossible. A friendship can accommodate different preferred activities within the same event. The interest in filming belongs to Tomoyo; it need not be rewritten as a sacrifice to make her sympathetic.
A different view can matter
Episode 21 has an injured Tomoyo notice a marathon-course anomaly from the sidelines.
Being unable to join the race does not make every kind of observation unavailable. The distinction is practical: following an activity from elsewhere can expose something that those occupied with performing it have not yet identified. This does not make injury beneficial. It makes the person who is injured more than the participation she has lost.
These two examples should not be collapsed into a single claim that Tomoyo always chooses the sidelines. In one, she selects what she wants to do; in the other, an injury restricts her. Her preference and her constraint have different causes. The connection is that her position still permits an active relationship with events.
Support is not the disappearance of a self
A generous friend can still influence a shared experience. Making clothes, choosing a recording role, and noticing a problem each bring a perspective of her own. Calling this pure selflessness would erase the particular interests that make Tomoyo's contribution hers.
These scenes also do not establish that she never directs Sakura or wants something for herself. Their smaller achievement is to make difference compatible with companionship. Tomoyo can be involved without duplicating Sakura, and a different position can add information instead of signaling indifference. The question of how a friend's resources shape an activity also appears in Becky's shopping trip with Anya.